微處理器 - STMicroelectronics STM32F103 - Assembly - I/O Toggle 21MHz

參考資訊：
https://sourceforge.net/projects/stm32flash/files/
https://stackoverflow.com/questions/59708656/stm32f103c8-gpio-speed-limit
https://electronics.stackexchange.com/questions/318658/stm32f103c8t6-maximum-io-output-speed

main.s

    .thumb
    .cpu cortex-m3
    .syntax unified

    .equiv GPIOA_CRL,    0x40010800
    .equiv GPIOA_CRH,    0x40010804
    .equiv GPIOA_IDR,    0x40010808
    .equiv GPIOA_ODR,    0x4001080c

    .equiv GPIOC_CRL,    0x40011000
    .equiv GPIOC_CRH,    0x40011004
    .equiv GPIOC_IDR,    0x40011008
    .equiv GPIOC_ODR,    0x4001100c

    .equiv RCC_CR,       0x40021000
    .equiv RCC_CFGR,     0x40021004
    .equiv RCC_APB2ENR,  0x40021018

    .equiv FLASH_ACR,    0x40022000

    .equiv STACKINIT,    0x20005000

    .global _start
    .section .text

    .org 0x0
    .word STACKINIT
    .word _start

    .org 0x100
    .align 2
    .thumb_func
_start:
    bl rcc_init
    bl flash_init
    
    ldr r4, =RCC_APB2ENR
    ldr r1, =(1 << 2)
    str r1, [r4]
 
    ldr r4, =GPIOA_CRH
    ldr r1, =(3 << 0)
    str r1, [r4]
 
    ldr r4, =GPIOA_ODR
    ldr r1, =0xffffffff
    ldr r2, =0x00000000
0:
    str r1, [r4]
    str r2, [r4]

    @eor r2, #(1 << 8)
    @str r2, [r4]
    b 0b
    
    .align 2
    .thumb_func
rcc_init:
    push {r4, lr}
    ldr r4, =RCC_CR
    mov r1, #(1 << 16)
    str r1, [r4]
0:
    ldr r1, [r4]
    tst r1, #(1 << 17)
    bne 0b

    ldr r4, =RCC_CFGR
    @mov r1, #(7 << 18) @ 72MHz
    mov r1, #(14 << 18) @ 128MHz
    orr r1, #(1 << 16)
    str r1, [r4]

    ldr r4, =RCC_CR
    ldr r1, [r4]
    orr r1, #(1 << 24)
    str r1, [r4]
0:
    ldr r1, [r4]
    tst r1, #(1 << 25)
    bne 0b

    ldr r4, =RCC_CFGR
    ldr r1, [r4]
    orr r1, #2
    str r1, [r4]
0:
    ldr r1, [r4]
    tst r1, #(1 << 3)
    bne 0b
    pop {r4, pc}

    .align
    .thumb_func
flash_init:
    push {r4, lr}
    ldr r4, =FLASH_ACR
    mov r1, #0x32
    str r1, [r4]
    pop {r4, pc}
    .end

PA8輸出


PLL 72MHz時，I/O Toggle可以達到12MHz，不過，stackoverflow的人說可以達到18MHz


PLL 128MHz時，I/O Toggle可以達到21MHz，不過，stackoverflow的人說可以達到36MHz


值得注意的是eor指令比str指令更耗時間，多了一倍指令週期，如下是PLL 128MHz時，使用eor指令的I/O Toggle速度